1. Field of the Invention
The present invention relates to devices and methods for imparting low frequency vibrations to a tissue of a subject to affect the autonomic nervous system of the subject, for example in order to treat disorders related to the autonomic nervous system of the subject.
2. Description of Background Art
The nervous system comprises the central nervous system (CNS), i.e. the brain and the spinal cord, and the peripheral nervous system, i.e. the nerves and ganglia outside of the brain and spinal cord. The peripheral nervous system is in turn divided into the somatic nervous system and the autonomic nervous system (ANS). In general, the somatic nervous system is associated with the voluntary control of organs such as skeletal muscles, whereas the automatic nervous system is largely associated with the unconscious control of internal organs and homeostasis.
The ANS, also referred to as the visceral nervous system, controls a number of vital functions in the body, for example heart rate and force of the contractions of the heart, constriction and dilation of blood vessels, respiration rate, digestion, contraction and dilation of the stomach, intestine and colon, the diameter of the pupils, urination, perspiration, sexual arousal, secretion from exocrine and endocrine glands, etc.
This control is achieved by a system of sensory (afferent) neurons and motor (efferent) neurons that form a feedback loop from and to the internal organs. Sensory neurons convey information regarding the state of the environment and of the internal organs, e.g. carbon dioxide and oxygen levels in the blood, chemical content of the gut, blood pressure etc, to the CNS. Motor neurons, on the other hand, convey information from the CNS to target organs in order to regulate or modify their activity. Through this feedback loop the sensory information constantly and unconsciously modulate the activity of the motor neurons of the ANS and thus the activity of the internal organs.
The motor neurons are located in clusters called “autonomic ganglia”. The efferent (motor) pathways of the ANS always involve two neurons; a myelinated preganglionic neuron that synapses onto an unmyelinated postganglionic neuron, the postganglionic neuron in turn innervating the target organ. A ganglion is a cluster of synapses between preganglionic and postganglionic neurons and comprises neural cell bodies and dendrites. The sensory neurons are also organized in similar ganglia.
The regulation and control of internal organs and of body homeostasis is also achieved through a balance between two subsystems of the ANS; the parasympathetic nervous system and the sympathetic nervous system. Most organs are affected by both these systems, which often have opposing, or rather complementary effects, on the organs. While the sympathetic nervous system is associated with arousal, energy, increased activity and decreased digestion, the parasympathetic nervous system is associated with rest, decreased activity and enhanced digestion.
There are several medical conditions related to dysautonomia, i.e. dysfunction of the ANS. Some of these are due to an imbalance between the sympathetic and the parasympathetic nervous systems, others have other causes. The symptoms may range from mild feelings of stress, fatigue, headaches, constipation and rapid heartbeats to stronger feelings of anxiety and dizziness. Severer diseases and syndromes include postural orthostatic tachycardia syndrome (POTS), inappropriate sinus tachycardia (IST), vasovagal syncope, mitral valve prolapse dysautonomia, pure autonomic failure, neurocardiogenic syncope (NCS), neurally mediated hypotension (NMH), orthostatic hypertension, autonomic instability and a number of lesser-known disorders such as cerebral salt-wasting syndrome. Other disorders associated with ANS malfunction include migraine, cluster headache, amyotrophic lateral sclerosis (ALS), Ménière's disease, Irritable Bowel syndrome (IBS), Crohn's disease, arteriosclerosis, ankylosing spondylitis (Bekhterev's disease), Sjögren's syndrome, torticollis, myotonic dystrophy, diabetes mellitus, ulcerative colitis, primary sclerosing cholangitis, asthma, inflammatory conditions of the distal colon, fibromyalgia, lumbago, and rheumatoid arthritis.
Management of conditions, symptoms and diseases depends on the severity of the symptom and the underlying cause. Some symptoms may be managed by adopting special diets, while others require medication. Often a combination of drugs is needed, commonly associated with unwanted side effects. There are also some known devices that have been developed in order to provide non-invasive and non-drug based methods for treating conditions related to the ANS. These are based on e.g. electrical stimulation, sound stimulation and ultrasonic stimulation.
Devices are known that by mechanical vibration affect tissue in a body cavity or over a body surface. In US 2008/0281238, a system for increasing activity on the fundamental brain is disclosed. The disclosed system comprises a first and a second vibration applying device, wherein the first vibration applying device applies vibrations having frequency components within an audible range to the auditory sense system of a living body. The second vibration applying device applies vibrations having super-high frequency components exceeding the audible range to another region of the body than the auditory sense system. The super-high frequency component of the second vibration increases the blood stream in the brain core and has the effect of enhancing the perception of the audible sound and improving the psycosomatic state of the patient.
in US 2010/0249637 A1 a device for treating restless leg syndrome is disclosed. The device comprises a sleeve to surround an arm or a leg of a patient and one or more vibration devices coupled to the sleeve. A motion sensing apparatus, in form of for example an accelerometer, an electroencephalography apparatus or an electromyography apparatus is used to monitor whether the arm or leg is about to move, in order to start the vibration stimulation before the patient becomes aware of the sensations that induces him or her to move his or her arm or leg.
US 2009/0005713 A1 discloses a method and device for using topically applied acoustic vibrations to treat different diseases and conditions. Low frequency vibrations are applied to the skin in order to stimulate production of adult stem cells.
in US 2002/0072781 A1 is shown and described e.g. various techniques for mechanical stimulation of vestibular nerves in the ear for the purpose of directly controlling respiratory system function. The stimulation can e.g. occur by an inflatable balloon exerting a static pressure on adjacent tissue. By varying the pressure, a certain sensation can be evoked. There is further shown and described another device for mechanical stimulation of nerves, which comprises a body that is vibrating at a certain frequency.
US 2004/0230252 A1 discloses a method and a device for affecting the ANS by a visual or audio stimulus. Information about the parasympathetic and/or sympathetic nervous system is obtained by monitoring the patient, and the information is used to continuously alter the stimuli according to the information obtained.
US 2005/0021092 A1 discloses a method of treating conditions related to abnormality in the ANS by increasing the parasympathetic activity/sympathetic activity ratio in a subject. An electrostimulatory device is used to stimulate an area in the parasympathetic nervous system and/or decrease the activity in the sympathetic nervous system. Information that is related to one or more aspects of the ANS is monitored before, during or after the electrical stimulation and the information may be used to trigger or modulate the stimulation.